WASHINGTON — Help wanted: Well-respected liberal jurist. Black. Female. Seniors need not apply.President Joe Biden’s search for a nominee to the Supreme Court isn’t just limited by credentials, race and gender. The reality for the nation’s oldest president — and for any president — is that for a lifetime appointment on the nation’s highest court, youth is particularly prized.It’s simple math. The younger Biden’s nominee, the longer she is likely to serve as a justice. The longer she serves as a justice, the longer liberals …